Hi ,
Looks like you would need a 2XDOW or interleaving stacking. Below is the DOW approach. BTW, please update your first post to include the additional rules addressed in your answer to PG, so that others who are interest in your question can get the whole story without digging into following every single posts.
data have;
infile cards truncover;
input Firm$ Year Director$ DateJoining;
cards;
A 1995 SAM 1982
A 1995 TOM 1996
A 1995 TINA
A 1995 ROB
A 1995 JACK
A 1996 SAM 1982
A 1996 TOM 1996
A 1996 TINA
A 1996 ROB
A 1996 JACK
A 1997 SAM 1982
A 1997 TOM 1996
A 1997 TINA
A 1997 ROB
A 1997 JACK
A 1998 SAM
A 1998 TOM 1996
A 1998 TINA
A 1998 ROB
A 1998 JACK
A 1999 SAM
A 1999 TOM 1996
A 1999 TINA
A 1999 ROB
A 1999 JACK
A 2000 SAM
A 2000 TOM 1996
A 2000 TINA
A 2000 ROB 2001
A 2000 JACK
A 2001 TINA
A 2001 ROB 2001
A 2001 JACK
;
data want;
do until (last.year);
set have;
by firm year;
_date1=min(_date1, datejoining);
_date2=ifn(datejoining=year,year,_date2);
_flag=ifn(datejoining=year,1,_flag);
if last.year then appt_date=coalesce(_date2,appt_date*_flag,_date1);
end;
do until (last.year);
set have;
by firm year;
output;
end;
retain _flag appt_date;
drop _:;
run;
proc print;run;
Haikuo
